The use of the frequency spectrum by various radio communication services was traditionally regulated in a static manner by the entities delegated with such regulatory function. However, this mode of operating leads to many frequency bands being under-occupied in time and space.
Research in the “cognitive radio” sector aims at defining a structure capable of allowing devices to temporarily and dynamically use such frequency bands without harming the authorized users or “primary users.” A cognitive radio is capable of analyzing the frequency spectrum and using the bands currently not used by their assignees (primary users). The approach of systems employing cognitive radios is that of generating—at the user level—an awareness of the state of the spectrum in such a manner to allow the radio receivers to move toward those bands that are vacant in that they are not currently used by the primary users.
Currently, the available literature concerning dynamic spectrum assessment regards methods in which a cognitive radio: i) independently carries out measurements on the spectrum, for example, detecting energy or other characteristics, and executes an algorithm to decide whether it can use some frequency bands to communicate; ii) contacts some server responsible for the spectrum management policy, capable of providing information regarding the availability of the spectrum alongside other information regarding management policy of the same; and iii) performs cooperative detection, where various cognitive radios exchange through any communication implementation, spectrum availability information.
Such approaches may reveal various drawbacks. For example, in the first approach considered previously, the information is of the local type, i.e. limited to the zone where the terminal is located, and there are widely known problems regarding hidden terminals and failed detections. Other methods use the presence of a centralized server, and they are based on a sort of spectrum micro-level “auction” and use an extensive information exchange between the various entities. The last mentioned method is also limited by the fact that the terminals participate in a cooperative manner. Furthermore, in all cases, the cognitive radios may include a spectrum detection capacity and/or may use the construction of an (generally expensive) additional infrastructure for spectrum detection and for forwarding the respective information.